Method and apparatus for correcting stack lean in a zig-zag folded web

ABSTRACT

Method and apparatus for correcting stack lean in a zig-zag folded web wherein a transverse force is cyclically applied to a traveling web so as to vary the motion of the web slightly as it passes through a transverse perforator.

This invention relates to a method and apparatus for correcting stacklean in a zig-zag folded web and, more particularly, to a web processedfor use as a business form.

Contemporary business forms are usually characterized by marginsequipped with line holes or other means for subsequent processingthrough a computer printer by the end user. The form manufacturing stepcan include lightly printed transverse lines (zones) which facilitatereading of subsequent computer printed data. The forms are manufacturedin large quantities at high speed, are zig-zag folded along lines ofcross perforation and are packaged in stacks before being sent to theend user.

A recurring defect in the manufacture of folded continuous forms isknown as stack lean. By this is meant the departure of a stack ofcontinuous forms (for example, 3,000) from true rectangularity. Thislean is either a sidewards lean or the one that is more difficult tocorrect, the forward/rearward lean. Forward/rearward stack lean iscaused by a minute difference in the length of alternate panels, andthis invention is directed to a controllable method for correcting saidlength differences to thereby control the forward or rearward stacklean. Beneficially this method can be applied selectively andindependently to each web while processing multiple plies, therebyovercoming limitations of prior art corrective means as applied tomulti-web, i.e., multiple plies or multiple width machines, as discussedin more detail hereinafter.

Lean is considered unacceptable by forms manufacturers because ofdifficulties in packaging and subsequent use. Some forms manufacturersspecify not more than one inch lean in a 12 inch high stack (3,000forms). Even as little a variation as 0.0004" in the perforation spacingin 81/2" long forms can cause stack lean to exceed this specification.Thus, one form 8.5004" with the next being 8.4996", and subsequent formswhich alternately vary by the same degree, will result in anunacceptable stack. Such a miniscule difference in the length ofalternate forms could be far less than the machine direction width ofthe perf cut, and in order of magnitude, less than the thickness of ahuman hair. As they apply to business forms machinery in general, thatis single web, multiple web or multi-width, two approaches have beenfollowed without success in attempting to correct this type of stacklean.

The first is to force a change in the fold line from its normal positionabout the center of the line of perforation. The other is to change theposition of the perforation itself.

Exemplary of the first approach is co-owned U.S. Pat. No. 4,204,669which attempted to "square" the stack by departing from the normal or"natural" fold line. By natural fold line, we refer to that location inthe web direction generally midway of the thickness of the perforationwhere the tiny bonds between perforations tend to fold under the impactof the folding tucker. This was achieved through the use of helicalgears on the folding rolls so that the timing between one set of foldlines was different from that of the adjacent set of fold lines.

The second unacceptable expedient made use of the same principle ofchanging the timing but applied this to the perforator. When applyingthis method, the perforating rolls normally have a circumference equalto two times the form length, with each roll having a perforating bladeand an anvil. The change in perforation spacing was achieved by indexingone perforator roll relative to the other to change the distance betweenadjacent perforations. With 1-wide single web processing this timingchange can be effective, but involves small acceleration anddeceleration forces that are difficult to control because of the highrotational inertia of the perforator. This expedient, however, isunacceptable in multiple width or multiple ply processing because thecorrective adjustment affects all stacking lanes equally. In effect,this expedient exerts control and influence on one lane but may exertunwanted correction to other stacking lanes thus adversely affectingwhat can normally be good stacks in said other lanes.

With the emphasis on high speed, high volume production, it is necessaryto process a web of more than one form width in the productionmachinery. For higher productivity, contemporary manufacturing practiceusually involves multiple width webs--usually three or four--while inother cases the manufacturers have superposed two or more webs andprocessed them simultaneously. The webs are then separated for foldinginto discrete stacks as seen in co-owned U.S. Pat. No. 3,596,899. Withmultiple superposed ply operation, the changing of the timing of theperforator could correct stack lean in one ply but not in the others.The same deficiency was true of the multiple width operation--it beingappreciated that to be competitive in production, the producing machinehad to process more than a single width web.

We have found that the difference in perforation spacing derives from anumber of factors. For example, the type of paper itself including thecharacter of the paper surface and variations in caliper across the webcan result in small, localized aberrations which throw off the line ofperforation. Web tension variations, manufacturing tolerances formachine gearing and folding rolls, runout of rolls, the stickiness ofthe ink, the engaging and disengaging of the line holes, the sharpnessand flexure of the perforation blades, etc., all may contribute minorbut in the aggregate, significant deviations which develop into stacklean.

In view of the prior unsuccessful expedients, the logical approach mightseem to have been to quantify the various defect producing factors andthus cure the problem at the source. However, we have discovered asimple, reliable method and apparatus for achieving this withoutattempting to correct for each of the many factors involved. Rather, theinvention involves a means to compensate for the sum of cumulativeerrors.

The invention solves the problem of forward/rearward stack lean eitherin side-by-side or superposed webs processing by cyclically changing themotion of each web going through the perforator, and thereby causeminute length changes to occur.

In one specific embodiment of the invention, an advancing web istransversely constrained on both sides (upstream and downstream) of theperforator and then cyclically applying a force in the web directionbetween one constraint and the perforator to induce a force in thelongitudinal web direction and thus change the motion of the web throughthe perforator.

According to the illustrated embodiment, a transverse force is appliedin cyclic fashion having an amplitude variation greater than theamplitude of the summation of the cyclic aberrations. By adjusting thetiming of the cyclic transverse force relative to the rotation of theperforator, the cyclic aberrations are compensated for, i.e., cancelled.Thus, instead of attempting to approximate very small aberrations andoppose them instantaneously, we introduce what could be considered amuch larger aberration and then time shift it to compensate for theaccumulated miniscule aberrations.

In the illustrated embodiment, this is achieved by an eccentric rolldownstream of the perforator but between two set of constraining pullrolls which in effect cyclically compensate for the above divertingfactors by lengthening and shortening the path of the web between theupstream constraint (such as the nip or constant tension roll before theperforator) and the downstream constraining means. This advantageouslengthening/shortening effect occurs in cyclic fashion over the periodof time required for two form lengths to pass the perforator, i.e.,three successive fold lines.

In the preferred embodiment, an eccentrically mounted or eccentricallydriven roll is arranged such that the maximum amount of eccentricity canbe phased to affect the shorter of two consecutive form lengths. For themaximum effect of incremental length increase to the short panel, theeccentric roll is phased so that the maximum (plus) eccentricity isapplied as the shorter of two forms passes through the cross perforator.

With this phased relationship, the maximum (minus) eccentricity appliesto the longest panel, and the summary effect is to apply maximum pluslength change to the shortest panel and the maximum minus length changeto the longest panel. The amount of this total plus and minus change maybe too great and, by means of the phase shifting device, a preselectedsharing or shifting of the plus (or additive) velocity change can beapplied to the short panel and a partial share of the subtractivevelocity change is made to apply to the same panel. Phase shifting ineffect is a means used to vary the magnitude of plus velocity change asit applies to the short panel and the magnitude of the subtractivevelocity change as it applies to the longer (adjacent) panel.

It will be understood that in the preferred embodiment, phasing isbenefically used as a finely controllable means to vary the magnitude ofadditive or subtractive velocity change as it applies to a given formlength, however, it is within the scope of this invention to use othermeans to vary the magnitude of velocity change per panel, including, butnot limited to variable web displacement means, variable web tensionmeans, etc.

In still other embodiments, the velocity (and web length) changing meanscan be arranged to act over a cycle greater than two formlengths--normally in even multiples. For example, another phenomenon,that is, a sine wave on both leading and trailing stack edges (referredto as "sawtooth") manifests itself in current production in a variationoccurring over 66 form lengths so that the term "cyclic" comprehendsvariations in motion over different frequencies depending upon thecorrection to be sought and this can be achieved in compound or tandemas well as single force applying means.

The invention is described in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a side elevational view, partially schematic, of apparatus forpracticing the invention;

FIGS. 2-4 are schematic presentations of a zig-zag folded stack;

FIG. 5 is an enlarged fragmentary side elevational view of one of themeans for cyclically changing web velocity;

FIG. 6 is a fragmentary sectional view taken along the segmental sightline 6--6 of FIG. 5; and

FIGS. 7-10 are graphs showing the operation of the invention.

DETAILED DESCRIPTION

In the illustration given and with reference first to FIG. 1, thenumeral 10 designates generally the frame of the inventive apparatus. Itwill be noted that FIG. 1 is a disjointed view in order to show theelongated machine without undue reduction in scale. In other words, theframe 10 continues from the left hand end of the upper portion to theright hand end of the lower portion.

In accordance with usual practice, the frame includes two side frameswhich can be appreciated from the sectional view in FIG. 6 as at 11 and12. The side frames provide mounting for the various gears, bearings,etc. employed to support and drive the various rolls to be describedhereinafter.

Referring again to FIG. 1, the numeral 13 designates a parent roll, theweb W of which is passed around a first idler roll 14 and thereafter asecond idler roll 15. The invention, in the preferred embodiment,contemplates a plurality of webs being processed simultaneously and forthat purpose a plurality of parent rolls (not shown) areprovided--suitably mounted on unwind stands in conventional fashion. Forexample a second web W_(a) passes around an idler 15a and a third webW_(b) passes around an idler 15b--still referring to the upper righthand portion of FIG. 1. Each web is drawn from its respective parentroll by a driven pull roll as at 16, 16a, and 16b.

In the illustration given, printing is not performed on the webs so theyare directed to further pull rolls 17, 17a and 17b. If desired, thesefurther pull rolls can be the impression cylinder of printing presses.Cooperating with the pull rolls 17, for example, is a nip providing roll18 (or a blanket roll) which serves to apply a constraint to the web W.Also provided on the frame 10 for each web is a cocking or skewing roll19 which serves to eliminate sideward lean.

Alternatively or cumulatively to the pull rolls, constant tension rollsas at 20, 20a and 20b may be provided in the paths of travel of each ofthe webs W, W_(a) and W_(b), respectively.

As the webs leave the last pull roll 17b or the web W_(b) leaves thelast constant tension roll, i.e., dancer roll, 20b, the webs aresuperposed for processing. For example, in the typical machine, a linehole punching unit 21 is advantageously provided, suitably mounted onthe frame 10. To develop the necessary cross perforations, a perforationunit 22 is provided slightly downstream of the line hole punching unit21. A second cross perforation unit 23 is normally provided so as todevelop a second size business form without having to change rolls. Forexample, in the illustration given, the perforation 22 has a knife rollequipped with three equally spaced apart knives and a circumference of251/2" so as to provide business forms 81/2" in length. The perforationunit 23 has a roll circumference of 33"--thereby being able to providethe other popular size of business form which has an 11" length. It willbe appreciated that when the perforation unit 22 is being employed, theunit 23 is inoperative--i.e., the cooperating perforating rolls arespaced apart so that the webs pass therebetween without any action beingperformed on them.

The superposed webs continue on through another processing station24--see the lower portion of FIG. 1 where file holes can be introducedinto the web simultaneously.

The webs are now processed separately in units for controlling the leanin a forward/rearward direction, the unit being designated generally25b, 25a and 25 proceeding from right to left.

Thus, the first encountered unit 25b handles the bottommost web W_(b).The second unit 25a handles the web W_(a) and the most downstream unit25 handles the web W. After passing through the units 25, 25a and 25b(the detailed structure and function of which will be describedhereinafter), the webs are again superposed, passed over an idler 26 andthrough a series of turning bars 27 so as to separate the webs incidentto going into a three wide folder generally designated 28. Thus, eachweb will generate its own stack. Each web is zig-zag folded as indicatedby the letters A and B and are conveyed away from the folder by creeperbelts 29 and thereafter to a stack delivery unit 30 at the extreme lefthand portion of FIG. 1. The invention also contemplates the processingof side-by-side webs--as well as those which are superposed. Forexample, the web may be equipped with longitudinally extending lines ofweakness (perforations or slits) downstream or upstream of the leancontrol roll. It is also possible to separate a web stack into twodiscrete stacks after folding by separation along thelongitudinally-extending lines of perforation.

It will be noted that the zig-zag folded web issuing from the foldingrolls has adjacent form lengths designated A and B. If the apparatus isoperating perfectly, i.e., the distance between adjacent perforationlines is identical, a rectangular shaped stack will be developed such asis illustrated schematically in FIG. 2 where the length of one form Aequals the length of the next form B. Two general aberrations ordeviations are possible--as illustrated in FIGS. 3 and 4 relative toforward and backward lean, respectively. To correct forward lean, it isnecessary to enlarge the form length B which function is performed bythe lean control unit 25 relative to the web W. It will be appreciatedthat with three zig-zag folded continuous web stacks issuing from themachine, various combinations of lean and no lean may occur. Thus, eachweb requires its own lean control unit.

Reference is now made to the second drawing sheet and, moreparticularly, to FIG. 5 which is an enlarged view in greater detail ofthe lean control unit 25 of FIG. 1. The front or left side frame of themachine is again designated 11 and the web W is seen to be proceedingfrom the right hand side of FIG. 5 around a lean control roll generallydesignated 31. Thereafter the web proceeds from the roll 31 after a 180°wrap thereon and around the capstan pull roll 32 and a further drivenroll 33 and thereafter forms a loop as at W'. A nip is formed betweenthe driven draw roll 33 and a nip roll 34 which--referring to FIG. 6--isa relatively narrow roll as compared to the full width draw roll 33.Thus, the rolls 32-34 form a nip or second constraint which, incombination with the constraint provided by the rolls 17 and 18 place apredetermined tension on the web W. The function of the lean controlroll 31 is to cyclically vary this tension or, more particularly,cyclically vary the velocity of the web W as it passes through theperforating means 22 or 23, as the case may be. For this purpose, thelean control roll 31 is interposed between the perforating means 22 or23 and the downstream constraining means 32-34.

The lean control roll 31 includes a shaft 35 (see FIG. 6) which isjournalled in bearings 36 provided in the side frames 11 and 12. Spacedoutwardly of the width of the web W, the shaft 35 is equipped withcollars 37 which have an eccentric exterior as can be appreciated fromthe different thicknesses illustrated in FIG. 6 at 38 and 39,respectively. Fixed to each collar 37 is a bearing 40. The outer shell41 of the lean control roll 31 is mounted on the bearings 40. Thus, thesurface of the roll 31 is adapted to rotate freely while the centerrotates eccentrically. The eccentricity is exaggerated in theillustration given, the center line of the shaft 35 being designated bythe numeral 42 while the center line of the shell 41 of the roll 31 isdesignated by the numeral 43. In the present practice of the invention,this will be of the order of 0.001" to about 0.004".

To drive the lean control roll shaft 35, it is equipped with a pulley 44which is connected by means of a cog belt 45 to a second pulley 46 onthe output side of a differential drive unit 47. Power to the input side48 of the unit 47 is derived from the main drive of the apparatus, i.e.,the drive which turns the various other driven rolls. The differentialdrive unit consists of bevel gears interconnected by a spider andplanetary gears (see the upper right hand portion of FIG. 6). A suitabledevice for this purpose is available from The Candy Manufacturing Co. ofChicago, Ill. under the designation "Dynamic Differential DD1A". Thedifferential drive turns the lean control roll shaft 35 at a rate of onerevolution for each two forms processed and allows the operator tochange the rotary phasing or timing of shaft eccentricity to perforatorwhile the machine is running--in order to control stack lean.

OPERATION

In the operation of the invention, the apparatus is equipped withseveral parent rolls and the webs, W, W_(a) and W_(b) are processedthrough the apparatus to result in discrete zig-zag folded continuousweb stacks in the stack delivery unit 30. In a tended machine, themachine operator views each stack and determines visually whether aforward or rearward lean is present. Alternatively, mechanical orelectrical sensing means can be employed for ascertaining the presenceof lean. If a lean is present, the setting on the differential speedunit is changed so as to vary the time relationship between theeccentric lean control roll 31 and the perforator 22. More particularly,if a forward lean is present (as exemplified by FIG. 3), the form lengthA is too long by a matter of a fraction of a thousandth of an inch orso--in contrast to the length of form B. This means that too much of theweb has passed through the perforating unit between the lines ofperforations defining the form length A and correspondingly, too littlebetween the time successive blades on the perforating roll have engagedthe web for defining form length B.

By rotating the eccentric portion (or shaft) of the lean control roll ata speed to make one revolution for each two form lengths and employingthe differential speed unit to change the timing between theeccentricity of the roll and the perforator, the position of the linesof perforation can be changed so as to bring about the stackconfiguration of FIG. 2.

The foregoing can be better understood by reference to FIG. 7. There thenumeral 49 designates a cyclic change of web velocity and the functionof time. For ease of illustration and understanding, this is presentedas a sine wave. In reality, all of the machine and paper variables canproduce a summation quite different than a sine wave--but inasmuch asthese are cyclic, the effect of the summation of these variables can berepresented by an equivalent sine wave.

The numeral 50 designates the desired web velocity V₀, a constant. Thedesignations P₁ and P₂, etc. refer to the locations of transverse linesof perforation developed by the perforator 22. It will be seen that thearea under the curve 49 varies between adjacent lines of perforation.This represents the length of the web passing through the perforator andit is greater between P₁ and P₂ than it is between P₂ and P₃. The areais the integral of velocity with respect to time, yielding length. Withthe illustrated condition, the length between P₁ and P₂ (A in theillustration given) is greater than between P₂ and P₃ (B in theillustration given).

According to the invention, a cyclic motion is introduced into the webhaving an amplitude variation considerably greater than the amplitudevariation of the summation of the machine variables, i.e., the foregoingaberrations represented sinusoidally as at 49. This is illustrated inFIG. 8 where a corrective motion designated 51 is shown. Through thedifferential drive 47 which permits phase or time shift, the rotationalpattern of the lean control roll shaft 35, substantially cancels out thesummation of the miniscule aberrations. For example, in FIG. 8, thecorrective motion represented by the curve 59 has a smaller area underthe curve at A (between adjacent perforation lines P₁ and P₂) than at B(between perforation lines P₂ and P₃).

The resultant of the two is represented graphically in FIG. 9 where theareas under the resultant curve 52 between adjacent perforations are thesame. Thus, the length of form between adjacent perforations is thesame--whatever portion of the curve 52 is below the constant velocityline is the same as that above--compare the cross hatched areas 53 and54.

How this is derived is represented graphically in FIG. 10. There, thenumeral 55 designates an area under the curve 49 and above the curve 50which is horizontally hatched and represents the length of the websegment A which is greater than desired, i.e., which creates the forwardlean. This extends between the points 56 and 57 which are theintersections of the curved V₀ between the perforation line P₁ and P₂.The corrective curve 51 has a greater amplitude (c being greater than e)and the phasing is different so that what the corrective motion wouldprovide is a length A which is shorter than desired, i.e., the areavertically hatched as at 58 (between points 60 and 61) being greaterthan the area 59 (horizontally hatched and lying between the points 61and 62). Through the adjustment of the phase or differential unit 47,the areas 55 and 59 are equal to the area 58. More properly, the areasare those below the respective curves and extending down to the baseline but in view of the very small magnitude of the variations incomparison with the total length, the distance between the curves andthe base lines has been foreshortened for convenience of depiction.

In the same fashion, the error curve 49 in the portion between the crossperforation lines P₂ and P₃, falls below the constant velocity line 50.This, without correction, would result in a form length B shorter thanthat desired. The corrective curve 51 has more area above the constantvelocity line 50 than it has below so that the summation will result ina positive correction exactly offsetting the error introduced by thecurve 49.

In the operation of the invention as illustrated, the phase shift θ isachieved through the use of the differential unit 47. In the normaloperation of the machine without any correction factor, the error curvewill usually assume a position wherein the form length A is differentfrom the form length B. Once the machine is running at a steady state,this small difference in form length will manifest itself uponaccumulation of error in a lean either forward or rearward. By the sametoken, the corrective curve resulting from the operation of the leancontrol roll 31 will normally not be such as to exactly compensate forthe length error. The only action required for correction of stack leanis that the machine operator starts the motor 63 (see the upper righthand portion of FIG. 6) so as to activate the ring gear 64 which in turnmoves the spider gearing 65 in a planetary fashion and thus changes theconnection between the bevel gears 66 and 67 connected to the input andoutput 48 and 46, respectively. Once the stack is balanced, the motor 63is stopped and a constant state operation is achieved wherein thephasing of the eccentric roll 31 is exactly compensatory (for allpractical intents and purposes) to the error accumulation due to machineand paper variables.

It will be appreciated that the invention is quite versatile,particularly where different form lengths are desired, i.e., 81/2"versus 11". By having the surface of the lean control roll 31 operate asan idler but eccentrically moving the center during a different timeperiod (by changing the drive ratio) the machine operation can bechanged from one form length to another without the need for changingthe lean control roll 31.

Alternative to the phase shifting provided by the eccentric lean controlroll 31, amplitude shifting can be utilized to advantage in the practiceof the invention--as by cyclically moving the roll 31 so as to increaseor decrease the length of the draw between the perforating means and thedownstream constraint. In any event, a transverse force is applied tothe web W to change its motion past the perforating means. Where twoconstraints are employed, this results in a change in the tension in theweb to compensate for the various aberrations built up upstream.However, where a constant tension roll is employed as at 20, the tensionremains constant but the motion still changes because of the impositionof the cyclic transverse force.

The invention also permits compensation for cyclic motion deviationsother than those occurring over two form lengths. If a second aberrationsuch as the 66 cycle variation mentioned above is to be compensated for,a compound input to roll shaft 35 can be employed with the output beingthe sum of the two cyclic inputs. Structurally, this is achieved byadding a phasing unit to provide a twice modified correction curve.

The invention is preferably practiced where the web tension iscontrolled by pull rolls although conventional pin belts can also beemployed. In such a case, there might be the tendency to enlarge theholes rather than increase the web velocity past the perforating unit.

While in the foregoing specification a detailed description of theinvention has been set down for the purpose of illustration, manyvariations in the details hereingiven may be made by those skilled inthe art without departing from the spirit and scope of the invention.

We claim:
 1. In a method for correcting stack lean in a zig-zag foldedcontinuous web having selected longitudinally spaced lines of transverseperforation and a fold at each said selected line, the steps of feedinga web through a means for transversely perforating the web while the webis under tension, and applying a cyclically varying additional force tothe web for the purpose of changing the longitudinal length between saidselected lines as the web passes through the perforating means, .Iadd.byproducing an amount of motion in said web passing through the saidperforating means greater than variables which cause a leaning stack,.Iaddend.the duration of .[.said.]. .Iadd.the .Iaddend.cycle of said.Iadd.cyclically varying additional .Iaddend.force extending at leastover the .Iadd.travel of .Iaddend.web length between three folds.Iadd.said cyclically varying force being a substantially continuouslyacting sinusoidal force and adjusting the cyclically applied force tocancel the amount of cyclic motion from the machine and paper variables,the adjustment of said cyclically applied force being achieved byadjusting the phase relationship between said cyclically applied forceand said cyclic motion resulting from the machine and papervariables.Iaddend..
 2. The method of claim 1 in which a plurality ofsuperposed webs are advanced through the perforating means, andindependently cyclically applying a force to each web for the purpose ofchanging the distance between selected perforations as the web passesthrough the perforating means.
 3. The method of claim 1 in which aplurality of side-by-side webs are advanced through the perforatingmeans, and independently cyclically applying a force to each web for thepurpose of changing the distance between selected perforations as thewebs pass through the perforating means.
 4. The method of claim 1wherein a web constraining means is applied before the web perforatingmeans and a second web constraining means is applied after the webperforating means.
 5. The method of claim 4 in which a force iscyclically applied perpendicular to said web between the perforatingmeans and one of said constraining means.
 6. The method of claim 4 inwhich one constraining means includes pulling the web downstream of saidperforating means so as to develop a predetermined tension therein, saidforce being operable to cyclically change the tension in said web. 7.The method of claim 4 in which one constraining means includes pullingthe web downstream of said perforating means, said force being operableto change the length of the path between said one constraining means andsaid perforating means.
 8. In a method for correcting stack lean in azig-zag folded continuous web having longitudinally spaced lines ofperforation, the steps of transversely perforating said web by advancingsame through a perforating means, constraining and advancing said web attwo longitudinally spaced points on opposite sides of the means forperforating the web, applying a .[.cyclically.]. .Iadd.substantiallycontinuously acting sinusoidally .Iaddend.varying force perpendicular tothe plane of said web to change the longitudinal length between thelines of perforation by producing an amount of motion in said webpassing through the said perforating means greater than the cyclicmotion resulting from the machine and paper variables which cause aleaning stack, .Iadd.the duration of a sine cycle of said forceextending at least over the web length between three folds, .Iaddend.andadjusting the .[.cyclically.]. .Iadd.sinusoidally .Iaddend.applied forceto cancel the amount of cyclic motion from the machine and papervariables .Iadd.while said web is being advanced, the adjustment of saidsinusoidally varying force being achieved by adjusting the phaserelationship between said sinusoidally varying force and said cyclicmotion resulting from the machine and paper variables..Iaddend. .[.9.The method of claim 8 in which said transverse force cyclic applicationis sinusoidal..].
 10. The method of claim 8 wherein said web is equippedwith longitudinally extending lines of weakness.
 11. The method of claim10 in which said longitudinally extending line of weakness is either aslit or a longitudinal perforation and occurs after one of saidconstraining points.
 12. The method of claim 11 wherein said web islongitudinally perforated and the resultant web separated into discretewebs after folding. .[.13. The method of claim 8 in which the adjustmentof said cyclically applied force is achieved by adjusting the timerelationship between said cyclically applied force and said cyclicmotion resulting from the machine and paper variables..].
 14. Apparatusfor correcting stack lean in zig-zag folded webs comprising means foradvancing a web under tension along a predetermined path, a perforatoroperably associated with said path for transversely perforating said webon approximately equally longitudinally spaced apart lines, and furthermeans operably associated with said path for applying a .[.cyclically.]..Iadd.substantially continuously acting sinusoidally .Iaddend.varyingadditional force to said web to cyclically and incrementally change thedistance between where preselected perforations will be made before saidweb is engaged by said perforator.Iadd., said additional force producingan amplitude of motion greater than the amplitude of the cyclic motionresulting from the machine and paper variables which cause a leaningstack, said additional force having a sine cycle whose duration extendsat least over the web length between three folds, said further meansincluding speed differential means for adjusting the phase relationshipbetween said additional force and said cyclic motion to cancel saidcyclic motion.Iaddend.. .[.15. The apparatus of claim 14 in which saidfurther means includes a roll for increasing the tension in said web..]..[.16. The apparatus of claim 14 in which said further means includesroll means for changing the web velocity by shifting the weblongitudinally..]. .Iadd.7. Apparatus for correcting stack lean in azig-zag folded web comprising a frame, means on said frame defining aweb path and web constraining means spaced apart in said path,aperforator in said path between said constraining means for perforatingsaid web on approximately equally longitudinally spaced lines, aneccentric roll rotatably mounted on said frame between said webconstraining means, and means operably associated with said frame forrotating said eccentric roll to provide a substantially continuouslyacting sinusoidally varying force on said web having a sine cycle whoseduration extends at least over the web length between three folds, saidsinusoidally varying force producing an amplitude of motion greater thanthe amplitude of the cyclic motion resulting from the machine and papervariables which cause a leaning stack, and speed varying means operablyassociated with said rotating means for changing the phase of saidsinusoidally varying force relative to the lines of perforation tocancel said cyclic motion..Iaddend. .Iadd.18. The apparatus of claim 17in which said speed varying means includes a differential drive unitinterposed in said rotating means..Iaddend. .Iadd.19. Apparatus forcorrecting stack lean in a zig-zag folded web comprising a frame, meanson said frame defining a web path and web constraining means spacedapart in said path, a perforator in said path between said constrainingmeans for perforating said web on approximately equally longitudinallyspaced lines to provide a form length between adjacent lines ofperforation, an eccentric roll rotatably mounted on said frame betweensaid web constraining means, said frame providing means to partiallywrap said web about said eccentric roll to provide constant web contacttherewith, means operably associated with said frame for continuouslyrotating said eccentric roll to provide a substantially continuouslyacting sinusoidally varying force on said web having a sine cycle whoseduration extends over an even number of form lengths, said sinusoidallyvarying force producing an amplitude of motion greater than theamplitude of the cyclic motion resulting from the machine and papervariables which cause a leaning stack, and differential means operablyassociated with said rotating means for changing the phase of saidsinusoidally varying force relative to the lines of perforation tocancel said cyclic motion..Iaddend.